Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter, arranged between the engine and the transmission, includes three primary components, an impeller, sometimes referred to as a pump, directly connected to the converter's cover and thereby the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine thereby providing additional rotational force to the pump.
As is well known in the art, a hub is often used to transfer torque between the turbine and the transmission input shaft. Various embodiments of hubs are used, and typically take the form of a cylindrical part having an internal spline arranged to engage a transmission input shaft and an external extension arranged to engage a turbine and/or spring retainer. Although using a hub of this type is perhaps the most common means of coupling the turbine to the transmission input shaft, this hub type is expensive to manufacture and introduces a significant amount of mass to the torque converter. The expense is in part derived from the large quantity of material that must be used to form a hub of this type, as well as the complexity from the added machining and finishing operations that are required. In short, the extension adds a substantial amount of cost to the hub because it requires more material and a larger die is required for forged or powdered metal pieces. Components may be joined to a hub with laser welding, however this also requires a radial extension and riveting.
FIG. 1 shows a front plan view of prior art torque converter 10, while FIG. 2 shows a partial cross-sectional view of torque converter 10 taken generally along line 2-2 of FIG. 1. Torque converter 10 includes studs 12 arranged to engage a rotary drive engine fly wheel (not shown), thereby imparting rotational force, i.e., torque, to the torque converter. Torque converter 10 is enclosed by front and back housing shells 14 and 16, respectively. Shells 14 and 16 are fixedly secured to each other by weld 18. Back housing shell 16 forms the body of pump 20. Pump 20 further includes blades 22 and core ring 24. Turbine 26 is disposed opposite pump 20 within the volume enclosed by housing shells 14 and 16. Turbine 26 includes turbine shell 28 which holds blades 30, which in turn are connected by core ring 32. Stator 34 is disposed between pump 20 and turbine 26, and blades 36 are arranged to redirect the flow of fluid (not shown) exiting turbine 26 prior to entering pump 20. During periods of use when the rotation of turbine 26 is less than the rotation of pump 20, stator 34 is prevented from rotating via the interaction between one-way clutch 38 and hub 40, as spline 42 of hub 40 non-rotatably engages a fixed shaft from a transmission (not shown), thereby preventing rotation of hub 40. As the ratio of rotational speeds between pump 20 and turbine 26 approaches unity, one-way clutch 38 permits stator 34 to freewheel, thus permitting it rotate at a speed substantially similar to pump 20 and turbine 26. As the drive engine supplies torque, housing shells 14 and 16 are rotated and thus pump 20 is also rotated. The rotation of pump 20 forces fluid from pump 20 into turbine 26, which in turn causes turbine 26 to rotate. The fluid passes through blades 36 of stator 34, is redirected, and subsequently returns to pump 20 to repeat the cycle.
Turbine shell 28, and thus turbine 26, is fixedly secured to spring retainer 44 and flange 46 of hub 48 via rivets 50. Rivets 50 are disposed within holes 52, 54 and 56 of flange 46, turbine shell 28 and spring retainer 44, respectively. Hence, as turbine 26 rotates, spring retainer 44 and hub 48 also rotate. Spring retainer 44 engages one end of spring 58 (not shown) while flange 60 of torque converter clutch 62 engages the other end of spring 58. Torque converter clutch 62 provides means to rotationally connect first housing shell 14 to hub 48. Thus, as the rotational speed of turbine 26 approaches that of pump 20, clutch 62 may be actuated, thereby compressively engaging friction material 64 with inner surface 66 of first housing shell 14. The engagement of clutch 62 provides a direct connection between the rotary drive engine and a rotary driven unit, i.e., transmission, thereby improving the efficiency of power transfer via the following path: first housing shell 14, friction material 64, flange 60, springs 58, spring retainer 44, rivet 50, flange 46, hub 48, spline 68 and lastly an input shaft of a rotary driven unit (not shown). Under such conditions, springs 58 act as vibration dampers, thereby reducing the transfer of engine power pulses.
FIG. 3 shows a front plan view of another prior art torque converter turbine 70 having turbine shell 71 wherein a plurality of blades 72, joined by core ring 74, are disposed. FIG. 4 shows a cross-sectional view taken generally along line 4-4 of FIG. 3, while FIG. 5 shows an enlarged partial cross-sectional view of the encircled region 5 of FIG. 4. Including flange 46 on hub 48 increases the cost to produce hub 48 due to the added material and the manufacturing processes which must be used to form such a configuration. In an effort to reduce the cost of producing a hub, alternative designs have developed. For example, in this prior art turbine, hub 76 is formed with shoulder 78 which provides an axial stop for drive plate 80. In this embodiment, various known means for retaining drive plate 80 to hub 76 may be used, e.g., welding or press fitting. Thus, in this instance, turbine 70 drives hub 76 via rivets 82, drive plate 80, and a weld (not shown) between drive plate 80 and hub 76.
Added mass can decrease the fuel economy of a vehicle. A torque converter must rotate in order to transfer torque between the engine and the transmission. Any mass added to the torque converter must also be rotated during this transfer process. Due to the principle of mass moment of inertia, i.e., a measure of a solid object's resistance to changes in rotational speed about its rotational axis, it can be shown mathematically that an object having a greater mass will have a greater mass moment of inertia. The mass moment of inertia I for a torque converter can be approximated by the following formula used for a thin disk having a radius r and a mass m:
  I  =            mr      2        2  Thus it can be seen that I is directly proportional to m, and therefore as m increases, I also increases. In view of this relationship between resistance to rotation, i.e., the amount of power required by the engine to drive the torque converter and the mass of the object rotating, the resistance to rotation may be decreased by removing mass from the torque converter, and thus increase the efficiency of power transfer from the engine to the transmission. It generally follows that removing mass from a torque converter hub, and thereby the torque converter, increases the efficiency of power transfer from the engine to the transmission.
As can be derived from the variety of devices and methods directed at coupling a torque converter turbine to a transmission, many means have been contemplated to accomplish the desired end, i.e., reliable, cost-effective coupling comprising easily manufactured parts, without sacrificing mass moment of inertia, and thus resulting in higher fuel efficiency and performance. Heretofore, tradeoffs between strength and reliability of coupling means, methods of manufacturing component parts and material mass for such means were required. Thus, there has been a longfelt need for a cost-effective torque converter hub having high strength and reliability, while introducing a minimal mass to the overall torque converter assembly, which is simple to manufacture.